Cardiac pacing devices typically aim to deliver pacing pulses to the heart at an energy level sufficient to cause capture without excessively draining power. For a variety of reasons, the energy level at which capture occurs may change over time. Consequently, so-called threshold search algorithms have been developed to help determine an energy level sufficient to cause capture. While such search algorithms may occur on a regular basis (e.g., daily basis), they may also be triggered by loss of capture.
To trigger a search algorithm based on loss of capture, some mechanism must be used to detect or infer loss of capture. However, conventional mechanisms can fail to discriminate fusion from loss of capture and hence may trigger a search where a search is not needed. Searches expend power and may not be well tolerated by some patients. Further, cardiac resynchronization therapy (CRT), which may rely on bi-ventricular pacing, can offer more opportunities for loss of capture. Yet further, a search can disturb CRT.
As described herein, exemplary mechanisms aim to increase accuracy of loss of capture detections or inferences. In addition, various exemplary mechanisms aim to distinguish fusion. Such mechanisms can allow for more consistent CRT therapy and help prevent unnecessary threshold searches. Various exemplary mechanisms described herein aim to satisfy these and/or other needs.